Collaborative Research: Evaluating hydrologic and ecologic responses to late-Glacial (9-33ka) abrupt climatic transitions in the coastal southwest United States

DESCRIPTION: Climate projections for the coastal southwestern United States predict a change in the frequency and magnitude of precipitation, perhaps with an overall drying. Despite the uncertainty in model projections, it is clear that any change to the region's winter dominated, "feast or famine" hydroclimatology will have consequences for the highly-populous, water-stressed region. This proposal develops a decadal to subcentennial scale, continuous sedimentary archive from Lake Elsinore, California using physical (grain size), biological (pollen), chemical (C:N), and isotopic (leaf wax hydrogen isotopes) analyses.

Characterized by exceptional resolution and archive continuity, this unique terrestrial site in the coastal southwest offers an unparalleled opportunity to evaluate hydrologic and ecologic change across abrupt climatic transitions during the late Glacial period (9-33ka). The cores will be characterized using a diverse, multi-proxy approach to capture large magnitude, late Glacial transitions, including leaf wax D/H shifts of >100 per mil, grain size evidence for variable run-off, and palynological evidence for changes in catchment vegetation. Lake Elsinore's exceptional archive is characterized by continuous deposition, high sedimentation rates, and the capacity for very high resolution radiocarbon age control using discrete organic material. Beyond representing a high quality archive of past terrestrial environmental change, Lake Elsinore sediments will enable proposed correlations with published marine reconstructions including local and distal marine records of Pacific sea surface temperatures (SSTs), as well as Atlantic SSTs and evidence for Meridional Overturning Circulation in order to assess the driving causes of the region's hydrologic and ecologic change. The team will focus on global abrupt climatic transitions including Heinrich events 1-3, and the transitions into and out of the Bolling-Allerod and the Younger Dryas. Although these transitions differ from the projected anthropogenic climate change, they offer large magnitude, abrupt transitions capable of providing maximum insights into forcing-response relationships. The working hypothesis is that hydrologic changes and ecologic shifts are closely in step and responding to local and global abrupt climatic transitions in the late Glacial to early Holocene. The questions are how much and how fast are these local responses demonstrated, and what might be the implications for the future.

The lead investigators institution, Cal State Fullerton, reaches a large number of minority, and especially Hispanic students. The proposal engages two female co-investigators, one of whom is an early career Assistant professor. The proposed study will provide training and research opportunities for graduate and undergraduate research at three institutions, with a focus on building the analytical and interpretative skill sets.

This research will also provide the first terrestrially-based, decadal to subcentennial scale record of how the vegetation of the coastal southwest responds to abrupt climatic transitions. The development of a baseline understanding of the causes, responses, and recovery of past hydrologic and ecologic change is of interest beyond the paleoclimate field with implications for ecologists, conservationists, and policy decisions pertaining to the California Floristic Biodiversity Hotspot.